1. Field of the Invention
This invention relates to heaters for electrically conductive liquids in which the liquid is heated by an electrical current between spaced electrodes located in the liquid.
2. Description of the Prior Art
Heating a conductive liquid, such as water, by passing an electrical current through it is known in the art. Heating of the liquid in response to the current is rapid and therefore electrode type heaters are particularly suited for mobile homes, portable homes, and recreational vehicles where a large quantity of water need not be heated and stored. An electrode type water heater may be of a small size, which is advantageous where space is limited.
In the conventional electrode type heater the electrodes are submerged at all times in the liquid. With this arrangement problems arise in controlling the current between the electrodes to regulate the heat of the liquid. One problem in the prior art is current surge, with commensurate line voltage drop, which occurs when a voltage is suddenly applied to electrodes located in a conductive liquid. A substantial part of the prior art is thus concerned with regulating the current in the liquid. In U.S. Pat. No. 1,293,964, current is regulated by mounting the electrodes on oppositely rotating bi-metallic springs to vary the distance between the electrodes. In U.S. Pat. No. 1,706,146, current is regulated by varying the length of the path the current must travel in the liquid by maintaining spacing between electrodes of opposite polarity while rotating the electrodes of one polarity away from the electrodes of the opposite polarity. U.S. Pat. No. 2,428,445, operates upon a similar principle. In U.S. Pat. No. 2,812,416, current is regulated by varying the depth of the electrodes in a liquid. U.S. Pat. No. 3,356,827, regulation of current in a liquid is accomplished by interposing a nonconductive shield between opposite electrodes. In U.S. Pat. No. 3,666,916, current is regulated by adjusting the distance between opposite electrodes in combination with a movable shield between the electrodes. In U.S. Pat. No. 3,053,964, of which the present applicant was co-inventor, current is regulated by adjusting an insulated shield between electrodes of opposite polarities. In U.S. Pat. No. 3,144,546, of which the present applicant was also a co-inventor, regulation is accomplished by moving an electrode or both electrodes from a position in the liquid to a position in a body of nonconductive gas disposed above the liquid. In U.S. Pat. No. 3,809,857, of which the present applicant is inventor, current is controlled by moving the electrodes into or out of the liquid to be heated in response to a change in temperature of the liquid. This is accomplished by mounting the electrodes on a counterbalanced buoyant cylinder and mounting a thermostatically controlled movable counterweight on the buoyant cylinder generally opposite the electrodes. In response to a change in temperature of the liquid in the tank, the movable counterweight moves away from the shaft which thereby shifts the center of gravity and rotates the shaft, rotating the electrodes into or out of the liquid. Slotted support guides receive shafts mounted with the buoyant cylinder to allow the cylinder to rotate and to float on the liquid as its level changes. While the apparatus of this patent is believed to be simple and effective, it is believed that the present invention will effect the same result in a different and improved manner.